Increased computer processing power generates increased heat. Increased processor density in computers concentrates this increased heat in a decreasing volume. The heat generated by the collocation of as many as 84 servers in one computer rack requires a cooling capacity unavailable from many of today's data center cooling systems. Data center cooling systems have been extensions of building air conditioning units used to cool office spaces. These computer room air conditioner (CRAC) systems have employed free-cooling as disclosed in U.S. Pat. No. 3,525,385 to Liebert in 1970. They use outside air to provide cooled room air. Cooled air alone can be insufficient to cool today's data centers. In addition to increased cooling needs, increased utility costs and demand for green business solutions apply increased pressure to find efficient sources for whatever amount of cooling is required.
Multiple figures of merit exist to quantify data center operation with respect to cost and efficiency. These include data center efficiency (DCE), power usage effectiveness (PUE), coefficient of performance (COP), module system efficiency (MSE), and power index (PI). This focus on metrics demonstrates that small improvements have a large impact on the bottom line of data centers. When multimillion dollar annual utility bills are involved, even fractional percentage changes save thousands and can provide rapid returns on investment.
Due to the reliability demands placed on most data centers, each component also needs to be highly dependable and should support back-up operation should a part of the cooling system fail.
There is a need to maintain improvements in computing power while reducing cost and environmental impact.